1. Field of the Invention
The present invention is in the field of die-casting metal alloys. More particularly, the present invention is in the field of die-casting aluminum alloys of low iron and high aluminum content.
2. Brief Description of the Prior Art
lt has been established practice in the prior art to die-cast aluminum alloys of relatively high iron content. Such an alloy is for example the "380 aluminum" which is well known in the art, and has the following approximate composition: 83.75% aluminum; 0.09% magnesium; 9.24% silicone: 2.86% zinc; 0.78% iron; 3.13% copper and 0.15% manganese. According to manufacturer's specifications "380 aluminum" may contain up to 1.0% iron.
As is known in the art and is also apparent from the abovegiven composition of "380 aluminum" alloy, the aluminum content of this alloy is relatively low, while the 0.78% iron content is considered high. "380 aluminum" or like low aluminum - high iron alloys have only mediocre mechanical and related metallurgic properties and are, generally speaking, not considered suitable for parts which must have high mechanical strength. For example, "380 aluminum" and like alloys are generally not considered suitable for fabrication of aircraft parts. Nor can "380 aluminum" or like aluminum alloys, be heat treated to significantly improve their mechanical properties.
On the other hand, "380 aluminum" or like aluminum alloys of high iron content have the significant advantage that they can be die-cast. As is known, die-casting is a process which is often utilized for relatively inexpensive mass production of a multitude of identical parts. Moreover, close tolerances and fine structural detail can be attained and reliably reproduced by die-casting.
lt is generally understood in the art that the relatively high iron content of "380 aluminum" renders it possible for this alloy to be die-cast. More specifically, it is understood that the high iron content of this or like alloys prevents sticking or soldering of the die-cast part to the steel die.
In contrast to the die-castable properties of "380 aluminum alloy", aluminum alloys having high aluminum and low iron content were not considered die-castable in the prior art even though these alloys have much more desirable mechanical properties than the "380 aluminum" alloy. Alcoa aluminum alloy A356.2 ("alloy 356") is an example of such an alloy, which contains more than 90% aluminum and no more than 0.12% iron. Alloy 356 has very desirable mechanical properties and is suitable for fabrication of parts requiring high mechanical strength. Alloy 356 can also be heat treated to improve its mechanical properties. Alloy 356 is suitable, for example, for use in certain aircraft parts.
Up to the present invention, however, the prior art has been unable to die-cast "alloy 356", or like aluminum alloys of high aluminum and low iron content. In this connection the experience in the prior art has been that when die-casting is attempted of such high aluminum and low iron containing alloys, the cast part sticks or solders to the steel die, making successful casting of the part impossible. It is widely believed in the art that the absence of sufficient iron from these high purity - high strength aluminum alloys causes the above-noted undesirable soldering phenomenon.
ln light of the foregoing, when manufacturing parts from "alloy 356" (or from like alloys) it has been necessary in the prior art to utilize the well known "investment casting" or "permanent mold casting" processes. A well known disadvantage of these processes, however, is that they are much less suitable for mass production than the die-casting process. Moreover, the investment casting and permanent mold casting processes are able to produce parts of lesser dimensional tolerances and having lesser fine details than comparable parts produced by die-casting.
Generally speaking, it has been estimated that die-casting an aluminum part, as compared to investment casting or permanent mold casting, can reduce the cost of the part approximately three to five fold while permitting production of parts having closer dimensional tolerances and finer detail. In light of the foregoing, there is a definite need in the prior art for a process for die-casting "alloy 356" and like alloys of high aluminum and low iron content. The present invention satisfies this need.